Frequent long-term cannabis smoking may have negative effects on a person’s verbal memory, a new study has found.
The study, conducted by researchers at the University of Lausanne, found that those who smoke cannabis daily over a period of five or more years had lower verbal memory — the ability to remember certain words — than those who did not smoke cannabis or smoked it less.
“We found a dose-dependent independent association between cumulative lifetime exposure to marijuana and worsening verbal memory in middle age,”
the authors of the study wrote.
Interestingly, the researchers observed that other areas of cognitive function, such as executive function or processing speed, appeared not to be affected by long-term cannabis use.
The study found the number of people who use cannabis daily was small. However, some drug policy experts have expressed concern that the loosening of cannabis laws — both on the state and federal level — could lead to a rise in use rates, and subsequently lead to more health problems.
The team of researchers examined data regarding the smoking habits of almost 3,400 Americans over a 25-year period. Following the study period, the test subjects submitted to a number of cognitive abilities tests. The tests included analyses on their memory and focus, among other areas.
New Study: ‘Genetic moderation of the effects of cannabis’
It isn’t exactly news to announce that connections have been found in the way cannabis effects individual consumers based on variations in their genetic makeup. But a new study published in the Journal of Psychopharmacology, conducted by researchers in the United Kingdom, points to an interesting correlation between a specific genetic variation and individual differences in cognitive and psychotic function upon ingestion of THC. Citing numerous past studies concerning cannabis and predisposition for psychosis and schizophrenia, the paper focuses on a gene well-studied with regards to THC, genetics, and individual vulnerabilities: catechol-O-methyltransferase, or COMT.
Naturally occurring changes in the sequence of a gene can impact the way two different people process the same chemicals. A commonly occurring genetic variation, or polymorphism, that affects the COMT gene is one known as Val158Met. According to the new paper, COMT affects the impact of THC on working memory performance differently in individuals with and without the Val158Met polymorphism. The paper, entitled ‘Genetic moderation of the effects of cannabis: Catechol-O-methyltransferase (COMT) affects the impact of Δ9-tetrahydrocannabinol (THC) on working memory performance but not on the occurrence of psychotic experiences,’ reports captivating findings relative to the cognitive effects of THC.
COMT is an enzyme that degrades dopamine in the brain, and the Val158Met genetic variation makes the COMT enzyme less effective at degrading dopamine. This means that individuals with this genetic variation have higher levels of dopamine, and higher levels of dopamine mean better working memory.
Study participants were administered THC or placebo intravenously by a psychiatrist. Following drug administration, researchers evaluated the working memory performance of participatory volunteers. What’s most interesting is that a difference in working memory performance following drug administration, “was not significant in Met carriers.” This is to say, those study participants with the Val158Met polymorphism were less likely to display a difference in working memory performance under the influence of THC than those without the popular genetic variant.
“In our participants, the administration of THC had little effect in Met carriers, impairing performance by ~12% compared with those given placebo (a difference that did not reach statistical significance). In contrast, Val/Val carriers given THC were dramatically impaired (~40%) compared with those given placebo.”
While the new study’s findings are consistent with past research exploring the relationship between COMT and THC, this study declares itself, “the largest to date to examine the impact of COMT genotype on the response to experimentally administered THC.”
Studies such as this serve as fuel for advancing underexplored areas of research, the results of which could drastically alter the way humans understand cannabis — and the way scientists understand humans.
Source: Tunbridge, E. M., et al. “Genetic moderation of the effects of cannabis: Catechol-O-methyltransferase (COMT) affects the impact of Δ9-tetrahydrocannabinol (THC) on working memory performance but not on the occurrence of psychotic experiences.” Journal of psychopharmacology (Oxford, England) (2015).